Deans pointed to Cooper's suspect defence, his positioning at fullback for the Queensland Reds, a reluctance to take contact in attack and an over-abundance of off-loads for being left out of his 25-man squad.

He also partly blamed Cooper's attacking shortcomings for the form dip of teammate Ben Tapuai.

"The truth seems to be (Deans) wanted to leave Cooper out because he doesn't trust him to do what the team requires," Slack wrote on the ninemsn website on Wednesday.

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"He probably should have said that, rather than blame Ben Tapuai's below-par form in 2013 on Cooper.

"The hurt and disappointment from the notorious toxic (outburst) of last year clearly still burns Deans, but for the sake of the team he needs to get over it.

"There is no doubt Deans gave Cooper a lot of support early in his career, but I believe he has run out of patience too soon and the exclusion of Australia's most talented flyhalf may well end up costing the coach his own job.

"Ask the Lions who they would least like to be wearing the Wallaby number 10 shirt and it would be close to a unanimous vote for Cooper."

Slack joins the likes of former Wallabies coaches Bob Dwyer, John Connolly and Eddie Jones as well as test backline greats Michael Lynagh and Tim Horan who have all strongly backed Cooper as the best playmaking candidate despite his weaknesses.

In contrast, there's been an absence of ringing endorsements for Deans' preferred choice at five-eighth, James O'Connor, who is more experienced in other backline positions.

Slack felt there were far more legitimate reasons to snub injury-plagued centre Rob Horne or inconsistent No 8 Wycliff Palu.

Deans can still include Cooper in his final 31-man squad when he adds six more players on June 11.

A 39-test centre from 1978 to 1987, Slack was also puzzled by the absence of a second halfback and the hints that France-based Luke Burgess, who has been a bench-warmer for Toulouse, would be added when he returns to Australia in the coming weeks.

"Deans' obsession with size and experience is understandable in certain positions, but I'm not sure halfback is one of them," he said. "And, in truth, Burgess has hardly been a consistently stellar performer for the Wallabies when he has played.

"The Brumbies' Nic White is no giant, but he has all the weapons to make an international number 9."